Vertical blinds generally include a horizontal carriage guide channel, an operating shaft extending lengthwise of the channel, a plurality of louver carriages mounted on the channel for movement therealong, each having a louver carrier mounted for rotation about an upright axis and carriage gear means engageable with the shaft and with the associated louver carrier for rotating the louver carrier in response to rotation of the shaft, drive housing at one end of the guide channel, a shaft turning mechanism mounted on the drive housing for turning the shaft, and carriage traverse means for moving at least a lead one of the carriages along the channel. Some prior vertical blinds for example as disclosed in U.S. Pat. Nos. 2,848,045; 2,993,535; 3,134,428; 3,280,891 and 4,657,060, used a cord or bead chain connected either directly or through gearing to a drive pulley at one end of the operating shaft to rotate the shaft in response to a downward pull on one or the other of the sides of the cord loop. However, the operating portions of the traverse cords for moving the louver carriages along the channel are commonly located at the same end of the channel as the louver rotating mechanism and this not only tended to cause tangling of the several operating cords and chains but also induced operator confusion as to which cord or chain should be manipulated to effect louver traversing and which should be manipulated to effect louver rotation. Some other vertical blinds for example as disclosed in U.S. Pat. Nos. 4,122,884; 4,214,622 and 4,386,644, used a wand that was connected through a gear mechanism to the operating shaft to rotate the operating shaft in response to turning of the wand about its lengthwise axis. The wands were usually connected through the operating shaft through a speed reducing gear drive, to minimize the torque required to rotate the operating shaft. However, this usually required rotation of the wand through a number of turns in order to rotate the louvers through 180.degree..
It has also been proposed as shown in U.S. Pat. Nos. 1,855,346 and 2,116,357 to tilt the head rail of a horizontal venetian blind using a wand connected to a lever attached to the head rail. However, such arrangements are only adapted for tilting the head rail through an angle of somewhat less than 180.degree., since the turning moment exerted by the vertically movable wand on the lever rapidly approaches zero as the lever is moved to either the top dead center or the bottom dead center position with respect to the head rail tilt axis.
In a vertical blind, the louvers must be rotated through substantially 180.degree. in order to move the louvers from a closed position in one direction to a closed position in the opposite direction. The operating shaft must transmit sufficient torque along its length to rotate all of the louvers through the associated carriage gears and there is a tendency for the operating shaft to twist under the torsional load on a long blind. The problem of twisting of the operating shaft is markedly aggravated when the gear ratio of the carriage gear mechanism is increased to rotate the louvers through a greater angle than the angle of rotation of the operating shaft and can cause incomplete closing of the louvers at the end of the blind remote from the drive end of the operating shaft. On the other hand, there is usually substantial backlash in the carriage gears so that the operating shaft must be rotated through a somewhat greater angle than the nominal gear ratio of the carriage gear mechanism would indicate. It has accordingly been common practice to provide a carriage gear mechanism in which the gear ratio between the shaft and louver carrier was 1:1 or less, and to provide either a bead chain or rotary wand type drive for rotating the operating shaft through an angle substantially greater than 180.degree..